Crystalline polyalkylene isophthalamide filaments with voids



United States Patent 3,325,342 CRYSTALLINE POLYALKYLENE ISOPHTHAL- AMIDE FILAMENTS WITH VOIDS Willard Hallam Bonner, Jr., Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, DeL, a corporation of Delaware No Drawing. Filed Mar. 19, 1963, Ser. No. 266,222 2 Claims. (Cl. 161-178) This application is directed to the non-elected invention disclosed in and is a continuation-in-part of my copending application, Ser. No. 52,028, filed Aug. 26, 1960, now US. Patent No. 3,088,794.

This invention relates generally to synthetic polyamide yarns and, more particularly, to the preparation of useful polyalkylene isophthalamide yarns.

Polyhexamethylene isophthalamide and polytetramethylene isophthalarnide are known in the art. However, when conventional spinning and drawing processes are applied to these polymers, an amorphous, non-oriented yarn having very poor properties results. Prior attempts to introduce both crystallization and orientation have failed.

It is an object of this invention to provide polyhexamethylene isophthalamide and polytetramethylene isophthalamide yarns having improved tensile properties, in particular, a higher modulus and tenacity. A further important object is to provide process improvements useful in the preparation of such yarns.

A specific object is the provision of a process for con verting a non-crystalline, unoriented, -as-spun polyhexamethylene isophthalamide or polytetramethylene isophthalamide yarn into a crystalline, oriented, drawn yarn.

With these and other objects in view, a crystalline and oriented polyhexamethylene isophthalamide or polytetramethylene isophthalamide yarn is provided by spinning the isophthalamide into an amorphous, unoriented asspun yarn, treating the as-spun yarn in an aqueous swelling agent thereby crystallizing it, and drawing the crystallized yarn to obtain a crystalline, oriented yarn. The yarn may then be boiled-off to further enhance its properties. The starting polymer may be prepared by interface polymerization or by melt polymerization, and the yarn may either be dry spun or melt spun.

In principle, the drawing step may be carried out at any temperature between room temperature and the melting point of the polyalkylene isophthalamide but, in practice a temperature between about 160 C. and about 200 C. is preferred. The preferred temperature range varies somewhat with the individual polymer. For polyhexamethylene isophthalamide, the preferred range is from about 160 C. to about 190 C. For polytetramethylene isophthalamide, the preferred temperature range is from about 185 C. to about 200 C.

The boil-off step is accomplished by immersing the drawn yarn on a bobbin in taut form, with the ends tied together, in boiling water for 5 minutes or longer. About minutes is convenient.

The swelling agent is a liquid which penetrates and plasticizes but does not dissolve the yarn. The preferred swelling agent for polytetramethylene isophthalamide is boiling water; for polyhexamethylene isophthalamide, it is preferably an aqueous solution of dimethylformamide (SO-% water). Other swelling agents do not appear to produce the level or type of crystallinity required for a highly crystalline oriented yarn. For example, heat treatment in an inert or non-swelling medium produces a different and less useful product, as will be shown herein-. after. The treatment with the swelling agent must be such as to insure that the liquid penetrates the yarn. The time required depends on the temperature employed. At room temperature, from one to 5 hours is desirable. At 55 0., about two minutes may suflice; at least 10 minutes is preferred. The treatment is preferably continued until maximum crystallinity is developed. The treatment may consist of immersing the yarn wound taut on a bobbin into a bath containing the liquid agent, immersing the yarn relaxed in skein form, or passing the yarn through the bath by means of rolls.

The drawn yarn product of the invention is characterized by having a low density of about 1 g./cc., as compared to a density of 1.24.25 g./cc. for the amorphous as-spun yarn. The lower density is: due to the presence of many microscopic voids produced by the swelling agent during the crystallization step, which voids remain after the swelling agent is removed. Because of these voids, the fiber is delustered, rendered more opaque, yet is readily dyed due to the open structure. In contrast to yarn which has been dry heat treated to induce crystallization, the yarn treated with aqueous swelling agents has higher tenacity and is essentially colorless.

The crystallinity index recorded in the examples is measured according to the procedure described by Wakelin, Virgin and Crystal in J. Appl. Phys., 30, 1954 1959). In this procedure, the most crystalline polymer sample obtainable is given a value of and the least crystalline sample a value of zero. The index for the various fiber samples is thus a relative measure of crystallinity between these two known extremes. To obtain the zero index for the polymers disclosed herein, the latter were spun into fibers which were amorphous to X-rays. To obtain the 100 index, a melt-pressed film was allowed to soak in an aqueous 50% dimethylformamide solution of ten minutes and then thermally annealed for six. hours at 200 C.

The orientation in the crystalline regions can be measured by the procedure of H. G. Ingersoll which is discussed in J. Appl. Phys., 17, 924 (1946). As reported herein, a low orientation angle is indicative of high orientation in the crystalline regions.

A recognized parameter for measuring toatl orientation is the percent molecular orientation at break elongation. This property has been described by W. H; Charch and W. W. Moseley in the Textile Research Journal, vol. XXIX, p. 525 (1959).

As noted previously,,the properties of the yarn are further enhanced by following the crystallizing step with a boil-off step. The crystallinity index: of polyhexamethylene isophthalamide yarn may be raised still further by following the boil-off taut treatment with a heat treatment at about C. at a tension that permits a slight retraction, for 5 to 10 minutes (Example IV).

Yarns prepared according to the teachings of the present invention find a useful application in the fabrication of tire cords as well as in carpets and apparel end uses. Their preparation and characterization are described in greater detail in the following examples.

' 3 '1 Example I To a 1-liter Waring Blendor under nitrogen is added a solution of 23.2 g. (0.2 mole) of distilled hexamethylenediamine (handled during weighing in a nitrogen atmos-phere) in 200 ml. of distilled water. To this solution is added rapidly, with high-speed stirring, a solution of 20.3 g. (0.1 mole) of pure isophthalyl chloride in 200 ml. of methylene chloride. The solid, White polyhexamethylene isophthalamide precipitates out of solution immediately as a large, solid mass and stirring becomes ineifective after about seconds. The solid product is removed from the blendor and soaked in acetone for several minutes, after which time it is again placed in the blender with approximately 500 ml. of acetone and cut up into small pieces resembling strips of wood shavings by the rapid stirring action of the blendor blades. The resulting product is then washed in the blendor with two 500 ml. portions of distilled water, once more with acetone and then dried in a vacuum oven at 100 C. for about 5 hours to give roughly 1718 g. of polyhexamethylene isophthalamide having an inherent viscosity in meta-cresol of 1.4.

About 4 0 g. of polymer, prepared by interface polymerization as described above, is dissolved in a solvent containing 50% by weight of freshly distilled trichloroethane, 4 9% formic acid and about 1% water to give a spinning dope containing 20% solids. Polyhexamethylene isophthalamide yarn is obtained from such a dope by the dry spinning technique using a column temperature of about 180-l90 C. to evaporate the solvent. The yarn is plied to 20 filaments and dried by standing in an exhaust hood. The yarn density is 1.25.

Theirs-spun yarn is then wound on a bobbin and soaked taut, with the ends tied together, in a 50% solution of dimethyl formarnide in water at the preferred temperature of 55 C. for 6 minutes to induce crystallization. The crystalline yarn is drawn at a draw ratio of 5.0 over a plate at 170 C. The drawn yarn is boiled off taut in water at 100 C. for minutes. The orientation angle, crystallinity index, and percent molecular orientation of the yarn are measured, as well as the tenacity, break elongation and initial modulus. Its density is about 1 and it is delustered. Similar values for a control yarn, which was not treated with a swelling agent, are included in the following table for purposes of comparison. It is noted that this control yarn has a density of 1.19, and is not delustered. The experiment was repeated, omitting the boil-off, and these results also are recorded in the table.

' TABLE Percent Crystal- Molec- Orienlinity ular tatlon T/E/Mi Index Orien- Angle tation As-spun 0 ab. 0 0.6/264/23 Drawn:

Crystalllzed 42 69 14 2. 8/11/70 Not crystallized- 15 46 0. 6/17/27 Boiled 015 after drai l crystallized 60 83 14 3. 8/ 14/75 Not crystallized- 60 7 150-180 0.4/17/26 Example 11 To a 1-liter Waring Blendor under nitrogen is added a solution of 17.6 .g. (0.2 mole) of distilled tetramethylenediamine (handled during weighing in a nitrogen atmosphere) in 200 ml. of distilled water. To this solution is added rapidly, with high speed stirring, a solution of 20.3 g. (0.1 mole) of pure isophthalyl chloride in 200 ml. of methylene chloride. The solid, white polytetramethylene isophthalamide precipitates out of solution after 15 seconds as a large, solid mass and stirring is continued another 2 minutes. The solid product is removed from the blendor and soaked in acetone for several minutes, after which time it is broken by hand into small pieces and washed in the blendor with water, acetone (two times) and water. After drying in a vacuum at C. for 5 hours, 16 g. (73%) of white polytetramethylene isophthalamide are obtained. The inherent viscosity in meta-cresol is 1.5.

About 40 g. of the polymer, prepared as described above, is dissolved in a solvent containing 40% by weight of freshly distilled trich'loroethane and 60% formic acid to give a spinning dope containing 23% solids. Polytetramethylene isopht-halamide yarn is obtained from such a dope by the dry spinning technique using a column temperature of about 180-190 C. to evaporate the solvent. The yarn is plied to 20 filaments and dried by standing in an exhaust hood.

The as-spun yarn is then wound on a bobbin and soaked taut, with the ends tied together, in boiling water for 30 minutes to induce crystallization. The crystalline yarn is drawn at a ratio of 5.0 over a pin at 195 C. The drawn yarn is boiled off taut in water at 100 C. for 30 minutes. The T/E/M values are 2.0/10/63. This yarn is delustered and has a lower density than the spun yarn prior to the boiling water treatment.

Example III Polyhexamethylene isophthalamide is prepared as follows: hexamethylene diammoniurn isophthalate salt in a methanol solution, pH 7.45, was heated with 0.2% boric acid for one hour at 231 C. under a nitrogen atmosphere, *followed by a two-hour nitrogen cycle at 265 C. and a one-half hour vacuum cycle (0.5 rnm.), also at 265 C. A pale yellow polymer having an inherent viscosity of 1.21.3 in meta-cresol is obtained and melt spun in a melt extruder at 340 C., 1,200 p.s.i., into a 5 filament total denier yarn at a spinning speed of 40 yards per minute. The melt spun yarn has a density of 1.19 and is bright. The as-spun yarn is crystallized and drawn according to the techniques of Example I and yarn with properties similar to those reported in the table is obtained. This yarn, like that of Example I, has a density of about 1, contains voids and is delustered.

Example IV Example V Filaments of polyhexamethylene isopht-halamide are prepared and spun as in Example I. They have a density of 1.24. The yarn is subjected to the treatments shown in the table and then drawn.

TABLE Crystalllnity Index 1 Draw Ratio] Crystallization Agent Temp. T/E/M A. 50% DMF in H 0; 10 min.

at 55 C B. Steam for 5 min 0. Dry N; at 180 C.,16 hr 68 5.5X/170 C..- 10 6.0X/ C 47 4.5X/ C 1 crystallinity of spun and treated yarn, before drawing. 2 Maximum operable draw ratio.

3 Tenacity, elongation and initial modulus of drawn yarn. 4 DMF=dimethyl formamide.

The drawn yarn C has a density of 1.20. When this yarn is subsequently boiled off taut, it has a density of 1.20, a crystallinity index of 68 and T/E/M, values of 2.5/ 13/54. Thus, in no case does the dry heat treated sample have the tenacity of the aqueous DMF treated yarn, nor does it have the void-containing, low density structure.

Having thus described the invention, What is claimed as new and desired to be secured by Letters Patent is:

1. A drawn filament comprised of a polyamide taken ,from the group consisting of polyhexarnethylene isophthalamide and polytetramethylene isophthalamide, said filament having a crystallinity index exceeding 40, a density of about 1 and voids therein giving it a delustered appearance, said filament also showing orientation in the crystalline regions as indicated by a low orientation angle.

angle is only about 14 and percent molecular orientation in the filament at break elongation exceeds 60%.

References Cited UNITED STATES PATENTS 2,880,057 3/1959 Cuculo l854 3,225,125 12/1965 Anderer et a1. 26450 OTHER REFERENCES Polyamide Resins, by Don E. Floyd, 1958, Reinhold Publ. Corp., pp. 10'0-1.

ALEXANDER WYMAN, Primary Examiner. JACOB H. STEINBERG, Examiner.

2. The filament of claim 1 wherein the orientation 15 M. A. LITMAN, Assistant Examiner. 

1. A DRAWN FILAMENT COMPRISED OF A POLYAMIDE TAKEN FROM THE GROUP CONSISTING OF POLYHEXAMETHYLENE ISOPHTHALAMIDE AND POLYTETRAMETHYLENE ISOPHTHALAMIDE, SAID FILAMENT HAVING A CRYSTALLINITY INDEX EXCEEDING 40, A DENSITY OF ABOUT 1 AND VOIDS THEREIN GIVING IT A DELUSTERED APPEARANCE, SAID FILAMENT ALSO SHOWING ORIENTATION IN THE CRYSTALLINE REGIONS AS INDICATED BY A LOW ORIENTATION ANGLE. 